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            <div><h3 class="title">
                <a name="asio.reference.io_context__strand"></a><a class="link" href="io_context__strand.html"
                                                                   title="io_context::strand">io_context::strand</a>
            </h3></div>
        </div>
    </div>
    <p>
        <a class="indexterm" name="asio.indexterm.io_context__strand"></a>
    </p>
    <p>
        Provides serialised handler execution.
    </p>
    <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">strand</span>
</pre>
    <h5>
        <a name="asio.reference.io_context__strand.h0"></a>
        <span><a name="asio.reference.io_context__strand.member_functions"></a></span><a class="link"
                                                                                         href="io_context__strand.html#asio.reference.io_context__strand.member_functions">Member
        Functions</a>
    </h5>
    <div class="informaltable">
        <table class="table">
            <colgroup>
                <col>
                <col>
            </colgroup>
            <thead>
            <tr>
                <th>
                    <p>
                        Name
                    </p>
                </th>
                <th>
                    <p>
                        Description
                    </p>
                </th>
            </tr>
            </thead>
            <tbody>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/context.html" title="io_context::strand::context"><span
                                class="bold"><strong>context</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Obtain the underlying execution context.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/defer.html" title="io_context::strand::defer"><span
                                class="bold"><strong>defer</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Request the strand to invoke the given function object.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/dispatch.html"
                           title="io_context::strand::dispatch"><span class="bold"><strong>dispatch</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Request the strand to invoke the given function object. <br>
                        <span class="silver"> —</span><br> (Deprecated: Use asio::dispatch().) Request the strand to
                        invoke the given handler.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/on_work_finished.html"
                           title="io_context::strand::on_work_finished"><span
                                class="bold"><strong>on_work_finished</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Inform the strand that some work is no longer outstanding.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/on_work_started.html"
                           title="io_context::strand::on_work_started"><span
                                class="bold"><strong>on_work_started</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Inform the strand that it has some outstanding work to do.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/post.html" title="io_context::strand::post"><span
                                class="bold"><strong>post</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Request the strand to invoke the given function object. <br>
                        <span class="silver"> —</span><br> (Deprecated: Use asio::post().) Request the strand to invoke
                        the given handler and return immediately.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/running_in_this_thread.html"
                           title="io_context::strand::running_in_this_thread"><span class="bold"><strong>running_in_this_thread</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Determine whether the strand is running in the current thread.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/strand.html" title="io_context::strand::strand"><span
                                class="bold"><strong>strand</strong></span></a> <span
                            class="silver">[constructor]</span>
                    </p>
                </td>
                <td>
                    <p>
                        Constructor.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/wrap.html" title="io_context::strand::wrap"><span
                                class="bold"><strong>wrap</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        (Deprecated: Use asio::bind_executor().) Create a new handler that
                        automatically dispatches the wrapped handler on the strand.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/_strand.html" title="io_context::strand::~strand"><span
                                class="bold"><strong>~strand</strong></span></a> <span
                            class="silver">[destructor]</span>
                    </p>
                </td>
                <td>
                    <p>
                        Destructor.
                    </p>
                </td>
            </tr>
            </tbody>
        </table>
    </div>
    <h5>
        <a name="asio.reference.io_context__strand.h1"></a>
        <span><a name="asio.reference.io_context__strand.friends"></a></span><a class="link"
                                                                                href="io_context__strand.html#asio.reference.io_context__strand.friends">Friends</a>
    </h5>
    <div class="informaltable">
        <table class="table">
            <colgroup>
                <col>
                <col>
            </colgroup>
            <thead>
            <tr>
                <th>
                    <p>
                        Name
                    </p>
                </th>
                <th>
                    <p>
                        Description
                    </p>
                </th>
            </tr>
            </thead>
            <tbody>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/operator_not__eq_.html"
                           title="io_context::strand::operator!="><span class="bold"><strong>operator!=</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Compare two strands for inequality.
                    </p>
                </td>
            </tr>
            <tr>
                <td>
                    <p>
                        <a class="link" href="io_context__strand/operator_eq__eq_.html"
                           title="io_context::strand::operator=="><span class="bold"><strong>operator==</strong></span></a>
                    </p>
                </td>
                <td>
                    <p>
                        Compare two strands for equality.
                    </p>
                </td>
            </tr>
            </tbody>
        </table>
    </div>
    <p>
        The <a class="link" href="io_context__strand.html" title="io_context::strand"><code class="computeroutput"><span
            class="identifier">io_context</span><span class="special">::</span><span
            class="identifier">strand</span></code></a>
        class provides the ability to post and dispatch handlers with the guarantee
        that none of those handlers will execute concurrently.
    </p>
    <h5>
        <a name="asio.reference.io_context__strand.h2"></a>
        <span><a name="asio.reference.io_context__strand.order_of_handler_invocation"></a></span><a class="link"
                                                                                                    href="io_context__strand.html#asio.reference.io_context__strand.order_of_handler_invocation">Order
        of handler invocation</a>
    </h5>
    <p>
        Given:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                a strand object <code class="computeroutput"><span class="identifier">s</span></code>
            </li>
            <li class="listitem">
                an object <code class="computeroutput"><span class="identifier">a</span></code> meeting completion
                handler requirements
            </li>
            <li class="listitem">
                an object <code class="computeroutput"><span class="identifier">a1</span></code> which is
                an arbitrary copy of <code class="computeroutput"><span class="identifier">a</span></code>
                made by the implementation
            </li>
            <li class="listitem">
                an object <code class="computeroutput"><span class="identifier">b</span></code> meeting completion
                handler requirements
            </li>
            <li class="listitem">
                an object <code class="computeroutput"><span class="identifier">b1</span></code> which is
                an arbitrary copy of <code class="computeroutput"><span class="identifier">b</span></code>
                made by the implementation
            </li>
        </ul>
    </div>
    <p>
        if any of the following conditions are true:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
                        class="identifier">post</span><span class="special">(</span><span
                        class="identifier">a</span><span class="special">)</span></code>
                happens-before <code class="computeroutput"><span class="identifier">s</span><span
                    class="special">.</span><span class="identifier">post</span><span class="special">(</span><span
                    class="identifier">b</span><span class="special">)</span></code>
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
                        class="identifier">post</span><span class="special">(</span><span
                        class="identifier">a</span><span class="special">)</span></code>
                happens-before <code class="computeroutput"><span class="identifier">s</span><span
                    class="special">.</span><span class="identifier">dispatch</span><span class="special">(</span><span
                    class="identifier">b</span><span class="special">)</span></code>,
                where the latter is performed outside the strand
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
                        class="identifier">dispatch</span><span class="special">(</span><span
                        class="identifier">a</span><span class="special">)</span></code>
                happens-before <code class="computeroutput"><span class="identifier">s</span><span
                    class="special">.</span><span class="identifier">post</span><span class="special">(</span><span
                    class="identifier">b</span><span class="special">)</span></code>,
                where the former is performed outside the strand
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
                        class="identifier">dispatch</span><span class="special">(</span><span
                        class="identifier">a</span><span class="special">)</span></code>
                happens-before <code class="computeroutput"><span class="identifier">s</span><span
                    class="special">.</span><span class="identifier">dispatch</span><span class="special">(</span><span
                    class="identifier">b</span><span class="special">)</span></code>,
                where both are performed outside the strand
            </li>
        </ul>
    </div>
    <p>
        then <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span
            class="special">(</span><span class="identifier">a1</span><span class="special">,</span>
        <span class="special">&amp;</span><span class="identifier">a1</span><span class="special">)</span></code>
        happens-before <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span
            class="special">(</span><span class="identifier">b1</span><span class="special">,</span>
        <span class="special">&amp;</span><span class="identifier">b1</span><span class="special">)</span></code>.
    </p>
    <p>
        Note that in the following case:
    </p>
    <pre class="programlisting"><span class="identifier">async_op_1</span><span class="special">(...,</span> <span
            class="identifier">s</span><span class="special">.</span><span class="identifier">wrap</span><span
            class="special">(</span><span class="identifier">a</span><span class="special">));</span>
<span class="identifier">async_op_2</span><span class="special">(...,</span> <span class="identifier">s</span><span
                class="special">.</span><span class="identifier">wrap</span><span class="special">(</span><span
                class="identifier">b</span><span class="special">));</span>
</pre>
    <p>
        the completion of the first async operation will perform <code class="computeroutput"><span
            class="identifier">s</span><span class="special">.</span><span class="identifier">dispatch</span><span
            class="special">(</span><span class="identifier">a</span><span class="special">)</span></code>,
        and the second will perform <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
            class="identifier">dispatch</span><span class="special">(</span><span class="identifier">b</span><span
            class="special">)</span></code>,
        but the order in which those are performed is unspecified. That is, you cannot
        state whether one happens-before the other. Therefore none of the above conditions
        are met and no ordering guarantee is made.
    </p>
    <h5>
        <a name="asio.reference.io_context__strand.h3"></a>
        <span><a name="asio.reference.io_context__strand.remarks"></a></span><a class="link"
                                                                                href="io_context__strand.html#asio.reference.io_context__strand.remarks">Remarks</a>
    </h5>
    <p>
        The implementation makes no guarantee that handlers posted or dispatched
        through different <code class="computeroutput"><span class="identifier">strand</span></code>
        objects will be invoked concurrently.
    </p>
    <h5>
        <a name="asio.reference.io_context__strand.h4"></a>
        <span><a name="asio.reference.io_context__strand.thread_safety"></a></span><a class="link"
                                                                                      href="io_context__strand.html#asio.reference.io_context__strand.thread_safety">Thread
        Safety</a>
    </h5>
    <p>
        <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
    </p>
    <p>
        <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
    </p>
    <h5>
        <a name="asio.reference.io_context__strand.h5"></a>
        <span><a name="asio.reference.io_context__strand.requirements"></a></span><a class="link"
                                                                                     href="io_context__strand.html#asio.reference.io_context__strand.requirements">Requirements</a>
    </h5>
    <p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">asio/io_context_strand.hpp</code>
    </p>
    <p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
    </p>
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            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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